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Sensors New age crystals

Nature volume 389, pages 784–785 (1997)Cite this article

The active elements in the new sensors are chemically functionalized gels. These gels are networks of crosslinked polymer strands, saturated like a sponge with a fluid solvent. Small changes in the fluid's composition can lead to dramatic changes in the gel's volume through a combination of processes known collectively as swelling. The degree to which a gel swells is controlled by a delicate balance of interactions between the polymer and its solvent, and between different chemical domains on the polymer itself. Changing the balance, for example by changing the gel's temperature, causes the polymer network to expand or contract.

Chemically functionalized gels can be tailor-made to respond strongly to a specific stimulus, such as the concentration of a particular ion in solution. The trick is to incorporate chemical groups into the polymer whose response to the desired stimulus induces a swelling transition. The functional groups highlighted in Holtz and Asher's study respond to specific chemical species by developing electrostatic charges whose mutual repulsion causes the gel to swell. Other gels swell in response to light2 or pH3. The response to these stimuli can be calibrated precisely and is highly reproducible.

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Figure 1: Leaded lights: a new gel sensor shows three drops of dilute Pb2+ solution, spreading slowly.

J. H. HOLTZ & S. A. ASHER

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  1. the James Franck Institute and in the Department of Physics, University of Chicago, 5640 S. Ellis Ave, Chicago, 60637, Illinois, USA

    David G. Grier

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  1. David G. Grier
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Grier, D. Sensors New age crystals. Nature 389, 784–785 (1997). https://doi.org/10.1038/39729

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